Solar Photovoltaic Power Conditioning Units

• US 20120063177A1
• Filed: 09/23/2011
• Published: 03/15/2012
• Est. Priority Date: 03/22/2011
• Status: Active Grant

• Current Assignee: Tesla Inc.
• Original Assignee: Enecsys Limited
• Inventors: Garrity, Paul
• Granted Patent: US 8,391,031 B2
• Time in Patent Office: Days
• US Class Current: 363/37
• CPC Class Codes: H02J 2300/24 of photovoltaic origin
• CPC Class Codes: H02J 2300/26 involving maximum power point tracking control for photovoltaic sources maximum power point systems in particular G05F1/67
• CPC Class Codes: H02J 3/381 Dispersed generators
• CPC Class Codes: H02J 3/40 Synchronising a generator for connection to a network or to another generator
• CPC Class Codes: H02M 5/458 using semiconductor devices only
• CPC Class Codes: H02M 7/44 by static converters
• CPC Class Codes: H02M 7/4807 having a high frequency intermediate AC stage
• CPC Class Codes: H02M 7/4815 Resonant converters H02M7/4811 and H02M7/4826 take precedence
• CPC Class Codes: Y02B 70/10 Technologies improving the efficiency by using switched-mode power supplies [SMPS], i.e. efficient power electronics conversion e.g. power factor correction or reduction of losses in power supplies or efficient standby modes
• CPC Class Codes: Y02E 10/56 Power conversion systems, e.g. maximum power point trackers

Abstract

We describe a photovoltaic power conditioning unit comprising: both dc and ac power inputs; a dc link; at least one dc-to-dc converter coupled between dc input and dc link; and a dc-to-ac converter coupled between dc link and ac output. The dc-to-dc converter comprises: a transformer having input and output windings; an input dc-to-ac converter coupled between dc input and input winding; and an ac-to-dc converter coupled between output winding the dc link. The output winding has a winding tap between the first and second portions. The ac-to-dc converter comprises: first and second rectifiers, each connected to a respective first and second portion of the output winding, to the dc link and winding tap; and a series inductor connected to the winding tap. Rectifiers are connected to the winding tap of the output winding via the series inductor wherein the series inductor is shared between the first and second rectifiers.

Claims

1. A power conditioning unit for delivering power from a photovoltaic dc power source to an ac mains power supply output, the power conditioning unit comprising:

a dc power input to receive dc power from a photovoltaic dc power source;

an ac power output for delivering ac power to said ac mains power supply;

a dc link coupled between said dc power input and said ac power output;

at least a first dc-to-dc converter coupled between said dc power input and said dc link; and

a dc-to-ac converter coupled between said dc link and said ac power output;

wherein said dc-to-dc converter comprises;

a transformer having an input winding and an output winding;

an input dc-to-ac converter coupled between said dc power input and said input winding of said transformer;

an ac-to-dc converter coupled between said output winding of said transformer and said dc link; and

wherein said output winding of said transformer has a winding tap between first and second portions of said output winding, and wherein said ac-to-dc converter comprises;

first and second rectifiers, each connected to a respective first and second said portion of said output winding, to said dc link, and to said winding tap; and

a series inductor connected to said winding tap; and

wherein said rectifiers are each connected to said winding tap of said output winding via said series inductor such that said series inductor is shared between said first and second rectifiers.

2. A power conditioning unit as claimed in claim 1 wherein said shared inductor comprises a winding on a core of said transformer.

3. A power conditioning unit as claimed in claim 2 wherein said first and second portions of said output winding of said transformer are windings on respective first and second legs of core said transformer, wherein a magnetic circuit of said transformer includes a shared core portion carrying flux from both said first and second legs of said core, and wherein said shared inductor comprises a winding on said shared core portion of said transformer.

4. A power conditioning unit as claimed in claim 3 wherein said shared inductor further comprises windings on said first and second legs of said core, each wound in an opposite sense to a sense of said winding on said shared core portion of said transformer.

5. A power conditioning unit as claimed in claim 1 further comprising a second said dc-to-dc converter coupled between said dc power input and said dc link.

6. A power conditioning unit as claimed in claim 5 wherein said input dc-to-ac converters of said first and second dc-to-dc converters comprise power switching devices to switch said dc power to said input winding of said transformer, said power conditioning unit further comprising at least one switching controller to control said power switching devices such that switching is synchronised between said input dc-to-ac converters.

7. A power conditioning unit as claimed in claim 6 wherein said switching is synchronised such that a phase angle between switching of corresponding said power switching devices in said input dc-to-ac converters is substantially 90 degrees or 180 degrees.

8. A power conditioning unit as claimed in claim 5 further comprising a dc conversion stage controller, coupled to sense an input or output power of said power conditioning unit and to control said first and second dc-to-dc converters, and wherein said dc conversion stage controller is configured to control, responsive to said sensed power, whether one or both of said dc-to-dc converters operates to feed dc power from said dc input to said dc link.

10. A power conditioning unit as claimed in claim 8 wherein said input dc-to-ac converters of said first and second dc-to-dc converters comprise power switching devices to switch said dc power to said input winding of said transformer, said power conditioning unit further comprising at least one switching controller to control said power switching devices such that switching is synchronised between said input dc-to-ac converters, and configured to switch off one of said dc-to-dc converters by gradually reducing said dc power fed to said dc link by the dc-to-dc converter.

11. A power conditioning unit as claimed in claim 10 wherein said dc conversion stage controller is configured to switch off one of said dc-to-dc converters by controlling a duty cycle of a pulse width modulated waveform controlling switching of a said power switching device.

12. A power conditioning unit as claimed in claim 10 wherein said dc conversion stage controller is configured to switch off one of said dc-to-dc converters by controlling a switching frequency of a said power switching device to gradually move said switching frequency away from a resonant frequency of a said dc-to-dc converter.

13. A power conditioning unit as claimed in claim 8 wherein said dc conversion stage controller further comprises a circuit to sense a level of ripple on a capacitor of a said input dc-to-ac converter to sense said power.

9. (canceled)

14. A photovoltaic power conditioning unit for delivering power from a dc power source to an ac mains power supply output, the photovoltaic power conditioning unit comprising:

a dc power input to receive dc power from a photovoltaic power source;

an ac power output for delivering ac power to said ac mains power supply;

a dc link coupled between said dc power input and said ac power output;

a dc-to-ac converter coupled between said dc link and said ac power output;

first and second dc-to-dc power converters, each coupled between said dc power input and said dc link and each having a series inductor in a connection between a said dc-to-dc power converter and said dc link; and

a dc conversion stage controller, coupled to sense an input or output power of said power conditioning unit and to control said first and second dc-to-dc converters; and

wherein said dc conversion stage controller is configured to control, responsive to said sensed power, whether one or both of said dc-to-dc converters operates to feed dc power from said dc input to said dc link.

15. A photovoltaic power conditioning unit as claimed in claim 14 wherein a said dc-to-dc converter comprises:

a transformer having an input winding and an output winding;

an input dc-to-ac converter coupled between said dc power input and said input winding of said transformer;

an ac-to-dc converter coupled between said output winding of said transformer and said dc link; and

wherein said output winding of said transformer has a winding tap between first and second portions of said output winding; and

wherein a said series inductor comprises an inductor connected to said winding tap.

16. A photovoltaic power conditioning unit as claimed in claim 15 wherein said series inductor comprises a winding on said transformer.

17. A photovoltaic power conditioning unit as claimed in claim 14 wherein said dc conversion stage controller is configured to switch off one of said dc-to-dc converters by gradually reducing said dc power fed to said dc link by the dc-to-dc converter.

18. A photovoltaic power conditioning unit as claimed in claim 17 wherein said first and second dc-to-dc converters comprise power switching devices to switch said dc power to said input winding of a respective said transformer;

and wherein said dc conversion stage controller is configured to switch off one of said dc-to-dc converters by controlling a duty cycle of a pulse width modulated waveform controlling switching of a said power switching device.

20. A photovoltaic power conditioning unit as claimed in claim 14 wherein said dc conversion stage controller is configured to inhibit operation of one of said dc-to-dc converters responsive to said sensed power being less than a threshold level.

19. (canceled)

21. A method of operating a power conditioning unit, the method comprising:

converting dc power from a photovoltaic dc power source to dc power for a dc link of said power conditioning unit using a pair of dc-to-dc power converters by converting said dc power to ac, providing said ac to a transformer and converting ac from said transformer to dc for said dc link;

converting dc power from said dc link to ac output power;

coupling dc outputs of said dc-to-dc power converters via one or more inductors to force load current sharing between said dc-to-dc power converters;

sensing a power level into or out of said power conditioning unit; and

inhibiting operation of a said dc-to-dc power converter responsive to said sensed power level to reduce losses in a core of said transformer of said dc-to-dc power converter below a threshold power level, and above said threshold power level reducing losses due to resistive heating in a said dc-to-dc power converter by enabling operation of both said dc-to-dc power converters.

22. A method as claimed in claim 21 further comprising forming a said inductor associated with a said dc-to-dc power converter as part of a said transformer of the dc-to-dc power converter.